1. Technical Field
This invention relates to steer axle assemblies and more particularly to a two boss steer axle assembly incorporating bearings to allow rotation of the kingpin.
2. Discussion of the Background Art
In a conventional steer axle assembly, a steering knuckle provides a spindle or bearing support for a wheel hub, bearings and wheel assembly. The steering knuckle is coupled to the steer axle using a kingpin. Typically, the steering knuckle has a forked yoke that defines first and second bosses with aligned bores. The yoke surrounds one end of the steer axle which defines a third boss having another bore aligned with the bores of the knuckle yoke. The kingpin extends through one of the knuckle bores, through the axle bore, and through the remaining knuckle bore to couple the knuckle and steer axle together.
In these conventional steer axle assemblies, the kingpin is fixedly coupled to the axle boss such that the kingpin does not rotate in relation to the axle boss. The knuckle pivots about the kingpin on a vertical steering axis. Typically, bushings are disposed within the aligned bores of the knuckle to allow the knuckle to rotate relative to the kingpin.
Conventional steer axle assemblies suffer from several disadvantages. First, conventional steer axle assemblies allow a relatively large amount of axial and radial movement of the kingpin. As a result of this axial and radial movement, the kingpin joints are subject to greater wear, thereby creating greater clearances and permitting the kingpin to shift and oscillate within the knuckle bores and reducing the useful lives of the assembly components. In order to limit axial and radial movement of the kingpin, shimming and precision machining of the steer axle assembly members are often required. Second, the use of a knuckle having a yoke (i.e., two bosses): (i) requires a relatively large number of seals; (ii) increases tooling, manufacturing, and assembly costs due to the relatively complex design; (iii) minimizes the ability to adjust the drop of the steer axle from the spindle; (iv) increases the size and weight of the assembly; and (v) prevents a predictable and relatively narrow tolerance range of bearing pre-load/endplay because assembly and vehicle loading causes deflection of bearings disposed within the bosses. Third, the use of bushings in conventional steer axle assemblies results in relatively large tolerances and often requires broaching or reaming of the bushings.
There is thus a need for a steer axle assembly that will minimize or eliminate one or more of the above-mentioned deficiencies.
The present invention provides a steer axle assembly.
A steer axle assembly in accordance with the present invention includes an axle beam defining a first boss with a first bore. The assembly further includes a knuckle having a body that defines only a second boss as compared to the conventional knuckle that defines second and third bosses. The second boss is in the form of a unitary sleeve from which a tie rod arm and steering arm extend. The second boss includes a second bore. The assembly further includes a set of bearings disposed in one of the first and second bores. In one embodiment of the invention, the bearings are disposed in the axle beam bore. In another embodiment of the invention, the bearings are disposed in the bore defined by the knuckle body. The assembly finally includes a kingpin. The kingpin is rotatably received within the bore having the bearings and is rigidly coupled within the bore that does not include the bearings. The kingpin may be tightened to its required specification via the use of a washer and nut on one end of the kingpin.
A steer axle assembly in accordance with the present invention represents a significant improvement as compared to conventional steer axle assemblies. First, axial and radial movement of the kingpin is diminished because such movement can be easily and consistently monitored and adjustedxe2x80x94without shimming or precision machining. Second, the two boss system of the inventive assembly provides for a simplified knuckle design and manufacture. The use of two bosses as opposed to three also provides: (i) improved life of the joint because of the decrease in the number of seals and necessary adjustments; (ii) decreased tooling, manufacturing and assembly costs; (iii) the ability to easily change the kingpin length and/or spacer size to change the drop in the axle beam thereby reducing the need for multiple gooseneck beam forgings with different gooseneck drops from the spindle to the beam spring pad or center section; (iv) a reduction in the overall size and weight of the assembly with the ability to accommodate a variety of brake styles and positions; (v) the ability to obtain a predictable and narrow tolerance range or bearing pre-load/endplay; and (vi) the ability to use structural steel of various cross-sections in addition to forged beams. Finally, the use of bearings, as opposed to bushings, within the boss bores provides: (i) the ability to obtain finer tolerances; (ii) a reduction in the variation in joint movement; and (iii) lower maintenance and manufacturing costs.
These and other features and objects of this invention will become apparent to one skilled in the art from the following detailed description and the accompanying drawings illustrating features of this invention by way of example.